The anti-rollback mechanism for manual wheelchairs disclosed in the prior patent application, while completely effective in its operation, is constructed with relatively expensive precision machine parts including sprag clutches and stainless steel races. This tends to reduce the overall practicality of the mechanism from a commercial standpoint.
Accordingly, it is the object of the present invention to provide a wheelchair anti-rollback mechanism of considerably greater simplicity, constructed from comparatively inexpensive components, such as bicycle brake pads and simple springs, all without loss of the full operational capability of the mechanism in the prior application. In fact, both mechanisms are operated in exactly the same manner by the occupant of a manual wheelchair. The less expensive mechanism embodied in this invention utilizes a simple over center linkage including component parts which can be stamped from sheet metal or molded from plastics.
An object of the present invention is to provide a wheel-chair anti-rollback mechanism which utilizes instead of an expensive one-way clutch a simple over center friction lock mechanism including a partial or complete brake drum fixed to the frame of the chair and cooperative pivoted over center brake shoes carried by the main wheel of the chair, together with simplified means to release the shoes when backward propulsion of the wheelchair is desired. As in the prior application, the mechanism normally allows only forward motion of the manual wheelchair as when traveling up an incline, thereby greatly reducing the effort expended by the user in powering the chair at this time. Without any anti-rollback mechanism on the chair, the user must exert a force on the propulsion ring with the hands and arms to counter the tendency for the chair to roll backwards on an incline. The extra energy required to prevent backward movement of the chair greatly increases the fatigue factor, especially when traveling up long inclines. The energy required is expended much more beneficially for producing forward motion only according to the invention.
Further objects of the invention are to provide an anti-rollback mechanism of decreased weight compared to previous designs, wherein the mechanism does not contribute to tire wear, and to utilize a self-locking friction mechanism as the heart of the anti-rollback system.
Other features and advantages of the invention will become apparent during the course of the following description.